The present invention relates to thermally developable photothermographic materials (hereinafter, also denoted as photothermographic materials) and in particular to photothermographic material exhibiting a higher maximum density and superior sharpness, improved in fogging under high temperature and high humidity and density unevenness in thermal processing, and an image recording method and an image forming method by the use thereof.
There are known a number of photosensitive materials comprising a support having thereon a photosensitive layer, which forms images upon imagewise exposure. Of these, techniques of forming images through thermal development are cited as a system suitable for environmental protection and simplifying image forming means.
Thermally developable photothermographic materials are disclosed, for example, in D. Morgan and B. Shely, U.S. Pat. Nos. 3,152,904 and 3,457,075, and D. H. Klosterboer, xe2x80x9cThermally Processed Silver Systemsxe2x80x9d (Imaging Processes and Materials, Neblette, 8th Edition, edited by J. M. Sturge, V. Walworth, and A. Shepp, page 2, 1969), etc. Such a photothermographic material contains a reducible light-insensitive silver source (such as organic silver salts), a catalytically active amount of photocatalyst (such as silver halide) and a reducing agent, which are dispersed in a binder matrix. Such photothermographic materials are stable at ordinary temperature and forms silver upon heating, after exposure, at a relatively high temperature (e.g., 80xc2x0 C. or higher) through an oxidation reduction reaction between the reducible silver source (which functions as an oxidizing agent) and the reducing agent. The oxidation reduction reaction is accelerated by catalytic action of a latent image produced by exposure. Silver formed through reaction of the reducible silver salt in exposed areas provides a black image, which contrasts with non-exposes areas, leading to image formation. Such photothermographic materials meet requirements for simplified processing and environmental protection.
In such a type photothermographic materials, acutance dyes and anti-halation dyes have been employed in the light-sensitive layer or backing layer to enhance sharpness. Specifically, in the light-sensitive layer, it was necessary to incorporate a light-insensitive organic silver salt as a silver source in a sufficient amount necessary to attain a sufficiently high maximum density. Further, to hold the light-insensitive organic silver salt and the reducing agent for the silver salt within the light-sensitive layer, a binder was needed in an amount equivalent to or more than these materials, resulting in a total dry layer thickness of 10 xcexcm or more. Although sharpness can be further enhanced by reducing the total dry layer thickness, decreasing the total dry layer thickness to 10 xcexcm or less with maintaining the maximum density of the light-sensitive layer results in increased fogging. It was proved that specifically when aged under high temperature and high humidity, fogging markedly increased.
There are known a system for thermally processing by bringing the protective layer into contact with a heat source such as a heated drum and a system for thermal processing by bringing the backing layer into contact with a heat source. However, when the foregoing photothermographic materials are thermally processed in these systems, it was proved that uniformity in developing density was markedly deteriorated.
Accordingly, it is an object of the present invention to provide a thermally developable photothermographic material exhibiting a higher maximum density and superior sharpness and improved in fogging under high temperature and high humidity and density unevenness in thermal processing.
It is an object of the invention to provide an image recording process and image forming process exhibiting little unevenness in density, even when bringing the protective layer and/or the backing layer into contact with a heated drum.
The above objects of the invention can be accomplished by the following constitution:
1. a photothermographic material comprising a support having on one side of the support a light-sensitive layer containing a light-sensitive silver halide, a light-insensitive organic silver salt, a reducing agent and a binder, and further thereon one or more protective layer(s), wherein the light-sensitive layer has a silver content of 0.10 to 0.45 g/cm3, the total dry light-sensitive layer thickness being 1 to 10 xcexcm and the total dry protective layer thickness being 3 to 20 xcexcm;
2. the photothermographic material described in 1, wherein the protective layer comprises at least two layers containing different binders and each having a dried layer thickness of 1.5 to 10 xcexcm;
3. the photothermographic material described in 1 or 2, wherein the photothermographic material has a backing layer having a dried layer thickness of 0.5 to 5 xcexcm on the opposite side of the support to the light-sensitive layer;
4. the photothermographic material described in any one of 1 through 3, wherein at least one of the protective layer and the backing layer contains colloidal inorganic particles;
5. the photothermographic material described in any one of 1 through 4, wherein the light-insensitive organic silver salt comprises tabular particles having an aspect ratio of 3 or more and exhibiting a number-averaged needle-form ratio of 1.1 to 10.0;
6. the photothermographic material described in any one of 1 through 4, wherein the light-insensitive organic silver salt is a silver salt of a polymer containing an acid group of 5 to 95% by weight;
7. the photothermographic material described in 6, wherein the light-insensitive organic silver salt is a silver salt of a polymer represented by the following formula (1) and/or a silver salt of a polymer formed through polyaddition of a mixture of a dihydric compound containing a carboxy group and an di-isocyanate compound;
xe2x80x94(A)axe2x80x94(B)bxe2x80x94xe2x80x83xe2x80x83formula (1)
wherein A represents a repeating unit derived from an ethylenically unsaturated monomer containing a carboxy group; B represents a repeating unit derived from an ethylenically unsaturated monomer except for A; a and b represent contents of A and B, respectively, a is 5 to 95% by weight and b is 5 to 95% by weight, provided that the sum of a and b is 100%;
8. the photothermographic material described in any one of 1 through 7, wherein the photothermographic material exhibits a total silver coverage of the light-sensitive silver halide and the light-insensitive organic silver salt of not more than 2.4 g/m2;
9. the photothermographic material described in any one of 1 through 8, wherein the photothermographic material contains an organic solvent of 5 to 1000 mg/m2;
10. an image recording method, wherein the photothermographic material described in any one of 1 through 9 is exposed by using a laser exposure apparatus, in which scanning laser light is not exposed at an angle substantially vertical to the exposed surface of the photosensitive material;
11. an image recording method, wherein the photothermographic material described in any one of 1 through 9 is exposed by using a laser exposure apparatus, in which scanning laser light is longitudinally multiple;
12. an image forming method, wherein the protective layer and/or the backing layer of the photothermographic material described in any one of 1 through 9 are brought into contact with a heat source to perform development.
The following mechanism is contemplated with respect to effects of this invention. Thus, it is supposed that fogging after storage under high temperature and high humidity, which is accelerated by decreasing the light-sensitive layer thickness is improved by increasing the protective layer thickness, employing plural kinds of binders or incorporating colloidal inorganic particles to form a stronger barrier between the light-sensitive layer and the external environment, lessening effects of humidity and leading to superior results. Further, it is supposed that with regard to unevenness in density, controls of the protective layer and backing layer result in enhanced uniformity in thermal transfer to the light-sensitive layer.